Guess who's returning for The Voice Season 8

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Riddle: Which two coaches have been on The Voice, but never at the same time?

While the current season of The Voice is still underway, NBC has already announced who the judges will be in 2015. Check out who's coming back.

Christina Aguilera and Pharrell Williams are both set to return to the hit singing contest to offer their expertise to hopeful talent. The Hollywood Reporter reports that they will be joining Adam Levine and Blake Shelton to form another amazing set of talent to coach contestants on their way to stardom.

The Voice has had a routine of changing out two coaches every other season, so Williams' return for a second year in a row came as a bit of a surprise. As for Aguilera, she took some time off from the show to take care of some very important business: having a baby girl.

In the interim, the current judges have been tearing it up in the red chairs. Gwen Stefani has been a fantastic addition to the group, while the bromance between Shelton and Levine has gotten some competition from the new bromance that's apparently forming between Levine and Williams. It's all very tawdry and we kind of love it.

Next season will be the first time viewers will get to see Williams and Aguilera on the show together. It will be interesting to see how the contestants choose between them and how the two will interact when it's time for the red chairs to spin around for the very first time.

President of alternative and late-night programming for NBC Entertainment, Paul Telegdy, summed up the excitement everyone at the network (and the fans as well, no doubt) had about the news.

"We are excited to welcome Christina back to her red chair and can't wait to see how she mixes things up among Adam, Blake and Pharrell in what will be an incredibly competitive competition," he said in a statement. "These four talented artists are at the top of their game as musicians and as coaches. The mentoring is sure to be intense, and the stakes will be high."